1. Field of the Invention
The present invention relates to a structure of a single-phase, claw pole type actuator and, more particularly, to a small, high-efficiency actuator that permits easy assembly and features a large detent torque and stable rotational repetitive operation.
2. Description of the Related Art
A so-called toroidal actuator with a toroidal winding wrapped around an annular core is known as an actuator for controlling angles by performing rotational repetitive operation. The toroidal actuator scarcely has a cogging torque and allows angle control to be achieved with good controllability and responsivity. The cogging torque is a torque produced when a coil is in a deenergization mode and hereinafter is referred to as xe2x80x9cdetent torquexe2x80x9d. The toroidal actuator, however, has various problems in that the toroidal winding is difficult to wind and has so small detent torque that energizing current must be kept flowing or a spring or the like must be used to forcibly urge the actuator at all times in an initial state wherein no energization is performed in an application wherein a given direction of operation must be always maintained.
For this purpose, there is also a cross-coil actuator that has a D-shaped soft magnetic material which forms a magnetic circuit and which covers an entire outer periphery of a single-phase winding unit so as to impart a detent torque. This type of actuator, however, is disadvantageous in that it exhibits poor magnetic circuit efficiency and inevitably becomes large and also poses a problem in that an external shape thereof cannot be circular.
Thus, there have been demands for a small, inexpensive actuator designed to have such functions and characteristics as operation of maintaining a rotor in a given direction by an appropriate detent torque in an initial state, and of performing a given operation for a period of time that corresponds to a time of energization of a coil, and of inversely energizing the coil to forcibly set it back to the initial state, although the actuator is not required to conduct accurate angle control by a closed loop.
The present invention has been made with a view to solving the problems described above, and an object thereof is to provide an inexpensive, small, high-efficiency actuator that has a single-phase claw pole structure, features easy assembly or winding, and is capable of activating a rotor in a certain given direction by a detent torque in a deenergization mode.
To this end, according to a first aspect of the present invention, there is provided a claw pole type actuator of a single-phase structure, comprising: a stator yoke composed of a pair of substantially circular planar yokes formed of a soft magnetic material, a number N of polar teeth which axially protrude from inner peripheral edges of the respective planar yokes and which are disposed to face each other, extending in an axial direction, and a cylindrical ring provided on outer peripheral edges of one of the planar yokes; an armature being constituted by installing a coil formed by winding a magnet wire in a coil receiving section shaped like an annular recess formed by the planar yokes, the polar teeth, and the cylindrical ring of the stator yoke; a rotor being concentrically disposed within the stator yoke and being adapted for repetitive rotational movement within a set angular range in response to energization of said coil, said angular range being less than 360xc2x0 and having its endpoints defined by a first angular position and a second angular position, and wherein said rotor is further adapted to be held in either said first angular position or said second angular position by a magnetic detent torque when said coil is deenergized, said rotor having a magnet, said magnet having a number N of magnetic poles; and a stator assembly which has flanges with bearings provided with a magnet for a magnetic field composed of a permanent magnet being installed to face the polar teeth of the stator with minute gaps provided therebetween; wherein the number of the polar teeth equals the number N of rotor magnetic poles (N is 2 or 4).
In a preferred form of the invention, the stator yoke is comprised of a first stator yoke in which a planar yoke and a polar tooth are combined into one piece, and a second stator yoke in which a planar yoke, polar teeth, and a cylindrical ring are combined into one piece, and the polar teeth in the first and second stator yokes are provide with the spacing of about respectively, are disposed at an interval of approximately 180 degrees in terms of an electrical angle.
In another preferred form of the invention, a pair of stator yokes, each being composed of the planar yoke and the cylindrical ring combined into one piece, are disposed to face each other.
In yet another preferred form of the invention, the rotation of the rotor is restricted by a stopper so that a maximum angle of the rotational motion stays within a range of 120/N to 240/N degrees (N is 2 or 4).
Preferably, the stopper is incorporated in the actuator.
In a further preferred form of the invention, a groove or a cut for destroying magnetic balance is provided on a central portion of one of the south pole and the north pole of the magnet for magnetic field.
In a further preferred form of the invention, the extensions of the two polar teeth in a circumferential direction are all the same and stay within a range of 220/N to 260/N degrees (N is 2 or 4) in terms of central angle.
In a further preferred form of the invention, air gaps in a radial direction formed by the polar teeth and the rotor magnet are uneven, and air gaps at central portions of the polar teeth are narrower than air gaps at ends of the polar teeth.
Preferably, the flange is composed of a nonmagnetic material.
In a further preferred form of the invention, a relationship between a detent torque Td (Nm) and a rated torque Trate (Nm) is as follows:
Trate/4xe2x89xa6Tdxe2x89xa63 Trate/4
where Trate denotes a maximum torque value obtained when a rated current is caused to flow, and detent torque Td denotes a maximum torque when a coil is in a deenergization mode.